# Questions tagged [raytracing]

Questions specific to raytracing (as opposed to scanline rendering), the 3D graphics technique of intersecting rays from the camera with objects in the scene.

230 questions
771 views

### What is the difference between importance sampling and mutiple importance sampling?

I can't understand math equations. I'm a graphic designer. What is "importance sampling"? What is "multiple importance sampling"? Could you explain easily, using illustrations and no math equations? ...
1k views

### Energy Conservation for Blinn-Phong BRDF

I am trying to sample from the Blinn-Phong BRDF. For testing, I use a spherical light source (Lambertian emission) sitting on a specular plane. Here's a reference image using energy-conserving Phong ...
286 views

### Ray Transformation to Object Space for Motion Blur

My raytracer supports a wide variety of objects. To intersect them, I use the standard technique of transforming rays into object-space. This works fantastically until I add motion blur. I model ...
254 views

### Can raytracing be used to imitate the behavior of light to a higher degree?

Raytracing "sees" the pixel on the other side of the screen; but doesn't this mean the rays traced can be computationally reflected and refracted imitating the properties of actual light? It'd be ...
373 views

### Problem with definition of BSDF and radiance

When I was reading theory behind physical based rendering I noticed that definition of BSDF and radiance has some problems. For example BSDF of purely specular surfaces is zero almost everywhere and ...
872 views

### Subpixel Rendering for a Ray Tracer

In font rendering, it is common to use subpixel rendering. The basic idea here is to break the pixel into its RGB components and then compute a value for each separately. Since each component is ...
1k views

### Ray Tracing with Cones: coverage, overlapping and abutting triangles

In his classic paper Ray Tracing with Cones, John Amanatides describes a variation on classical ray tracing. By extending the concept of a ray by an aperture angle, making it a cone, aliasing effects (...
1k views

### How to raytrace Bezier surfaces?

I tried this question on math.SE and surprisingly, the answer was "the equations are too nasty, just feed the function it to a numerical root-finder". But if you consider yourself "a graphics guy" ...
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### Why is recursion forbidden in OpenCL?

I'd like to use OpenCL to accelerate rendering of raytraced images, but I notice that the Wikipedia page claims that recursion is forbidden in Open CL. Is this true? As I make extensive use of ...
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Radiosity is basically what allows this: In a tutorial of Cornell University about Radiosity it is mentioned that: A ray-traced version of the image shows only the light reaching the viewer by ...
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### Can I raytrace gravitational lensing using only a single point source of gravity?

I'd like to simulate the magnification of very distant objects by the lensing effect of a less distant galaxy. Will I need to model large numbers of point masses or can I get away with just a single ...
982 views

### How to build a decent lens/camera objective model for path tracing?

I have written a small path-tracer after learning and experimenting on smallpt. The only thing that I did not write (and understood) myself is how the initial rays are computed and fired from the ...
696 views

### Non Real Time Raytracing

I've played with real time raytracing (and raymarching etc) quite a bit, but haven't spent that much time on non real time raytracing - for higher quality images or for pre-rendering videos and the ...
2k views

### How are volumetric effects handled in raytracing?

How are volumetric effects such as smoke, fog, or clouds rendered by a raytracer? Unlike solid objects, these don't have a well-defined surface to compute an intersection with.
117 views

### Ray-based rendering terms [closed]

There are a number of terms for rendering techniques based on the particle model of light: forward ray-tracing, reverse ray-tracing, ray-casting, ray-marching, and possibly others. What's the ...
353 views

### What is “tiled” raytracing?

I've seen mention of tiled raytracing, but haven't been able to find much on google about it. Can anyone explain what it is and how it works?
587 views

### Multiple Importance Sampling with more than one light

(Note: This has been cross posted from my ompf2 post.) Recently I've implemented Multiple Importance Sampling for the sampling of surfaces in my ray tracer. I do this by, on each intersection, ...
363 views

### Speeding up convergence: am I reinventing the wheel?

I'm trying to learn about raytracing by implementing things in Python 3. I know this is always going to be slower than something like C++, and I know the speed could also be improved by using GPU ...
832 views

### Why are inverse transformations applied to rays rather than forward transformations to objects?

When computing ray-object intersections against a transformed object, most raytracers apply the inverse transform to each ray and compute the intersection against a non-transformed object. Wouldn't ...
1k views

### Am I missing something for ambient occlusion?

I'm trying to implement ambient occlusion in Python 3 and I'm seeing shadows beneath my reflective spheres but they seem very faint. I'm not sure if that means I've missed something, or if I just have ...
542 views

### How do correlated samples influence the behavior of a Monte Carlo renderer?

Most descriptions of Monte Carlo rendering methods, such as path tracing or bidirectional path tracing, assume that samples are generated independently; that is, a standard random number generator is ...
10k views

### What is Ray Marching? Is Sphere Tracing the same thing?

A lot of ShaderToy demos share the Ray Marching algorithm to render the scene, but they are often written with a very compact style and i can't find any straightforward examples or explanation. So ...
217 views

### How can I raytrace a scene that does not fit into memory?

If the scene to be raytraced cannot be stored in memory, then without adding more RAM to the machine it seems unrealistic to render it in a practical time span, due to the need to load different parts ...
72 views

### Can I parallelise the scene for a raytraced image, rather than just the pixels?

Raytracing an image can be performed in parallel by calculating the colour of different pixels on different machines. However, this still requires each machine to have access to the entire scene to be ...
385 views

### Modelling Young's double slit experiment

Young's double slit experiment is very simple to set up and simple to explain, but it is an example of both diffraction and interference, neither of which are modelled by conventional raytracing. It ...
252 views

### Polarising reflection and refraction for a wrap around water surface

I want to render realistic images of water in an orbiting space habitat. The image does not need to be generated in real time, although I wouldn't want it to take weeks either. I'm looking for an ...
201 views

### Can I accelerate rendering an image from a ray cloud using a GPU?

Start with a precalculated "ray cloud" - the starting point and direction of a large number of rays, most of which will not contribute to the image. The image plane's position and orientation are then ...
79 views

### What are the side effects of biasing brightness in continuous spectrum raytracing?

I want to model rays with a continuous range of frequencies so that I can get raytraced images with colour separation on refraction. I can model a light source with a specified frequency distribution ...